Add AnnotationIntrospector.resolveSetterConflict(...) to allow custom setter conflict resolution

[cowtowncoder]

(note: inspired by #1033)

Although Jackson tries to figure out reasonable rules for precedence of setter to use, in case of overlap, it is not possible to resolve all kinds of application/usage-specific cases. So to allow plugging in custom handling, let's add a mechanism overridable via AnnotationIntrospector that makes it possible to resolve at least some of most common cases.

In addition, JacksonAnnotationIntrospector should implement very basic heuristics, where:

• Primitive type has higher precedence than non-primitive
• For other types, java.lang.String has precedence over other non-primitive types.

This logic is overridable.